In the fabrication of micro-electronic devices such as integrated circuits or liquid crystal displays, a substrate has to go through a number of fabrication steps, including wet etching, wet cleaning or rinsing.
In the documents U.S. Pat. No. 5,271,774 and Japanese Patent JP-A-07211686, methods are described to remove a liquid from the surface of a substrate by applying a gaseous substance to the substrate, which, when mixed with the liquid, reduces the surface tension of the liquid, so that it can be easily removed from the surface by a centrifugal force, i.e. by subjecting the substrate to a rotary movement. However, these methods are only applicable to the substrate as a whole, and cannot be used for local treatment of the substrate. Document EP-A-817246 is describing an apparatus and method for wet cleaning or etching of flat substrate surfaces, whereby a substrate is moved through a stationary amount of liquid. This method is also related to a treatment of the substrate as a whole, not of a local zone of said substrate.
During some processing steps, an annular edge area of the substrate is treated, for example for the removal of certain layers, like a resist or a metal film (e.g. Cu). Sometimes, it is only the outer rim of the substrate which is treated, while the top and bottom surfaces of the substrate must remain untouched.
Techniques exist whereby a beam of liquid is directed to the edge area or the rim of a rotating substrate in order to perform these process steps. However these existing techniques offer a poor protection of the substrate surface against the cleaning liquid. It would therefore be advantageous to find a way of protecting the substrate surface while treating said annular edge area or its outer rim with a liquid. Another disadvantage of existing techniques is that the rotational speed of the substrate during processing must be relatively high, which is particularly problematic for large substrates.
Some processing steps require the removal of larger sized features from the substrate surface, e.g. for revealing underlying zero markers, which are used for the accurate lateral positioning during processing, e.g., during photographic exposure. Although the definition of the zero markers themselves requires high accuracy, the accuracy requirements of the window for removing a layer on top of the zero markers can be fairly relaxed. So far in the state of the art, the use of a photo resist step is mostly used to accomplish these areas. By using a photo resist step, a patterned protective resist layer is obtained on the substrate surface. The pattern is such that the areas to be etched are not covered with resist. After this, the substrate is etched and the photo resist layer is removed. This is however an expensive and time-consuming effort.
An alternative way of producing such larger sized areas which are free of film, consists of a local shielding by shielding plates during film deposition. However, this technique leads to an increased risk of particle contamination and scratch formation on the substrate. Furthermore, this shielding technique is not generally applicable. It requires compatibility of the shielding plates with the deposition process of interest. To produce these larger sized features, it would therefore be advantageous to find a method that allows less accuracy but lower cost and higher processing speed, without creating any particle contamination.
Document JP-A-11166882 describes a pre-concentration or collection technique, used in contamination measurements for semi-conductors. It is a technique, whereby a droplet is moved over the substrate surface, in order to collect contaminants and subsequently analyze their concentrations. Currently, this technique is mainly used on silicon surfaces, by rendering the surface hydrophobic by way of an HF-treatment. This way, the water-based droplet is contained. The technique is however not confined to silicon surfaces. In some cases, it has been observed that the contact angle between the droplet and the substrate surface is insufficient. Furthermore, it would be advantageous to find a method whereby, in the case of silicon surfaces, the extra processing step of providing an HF-treatment would become unnecessary.
Document U.S. Pat. No. 5,492,566 describes a way of holding a substrate to a flat surface by way of the Bernoulli effect. By supplying a gas at a high speed between said substrate and said surface through an annular nozzle, a pressure drop will result, under said substrate, thus holding said substrate to said surface. Substrates held in this way can be subjected to various wet treatment steps, like cleaning or etching. However, a danger exists of liquid attaching itself to the rim or the backside of the substrate.